A projector is generally placed on a horizontal plane such as a desk or a ceiling, and projects an image on a screen installed on a vertical plane such as a wall. In such a case, a posture or the like of the projector is adjusted so as to project a clear image on the screen.
However, not all the projectors can be installed to have a perpendicular relation between the installation surface and the screen surface. For example, when installed in a large step-like hall, the projector installed on the ceiling projects an image downward to the screen on the front wall of the hall, and thus the image is distorted trapezoidally. Furthermore, a portable projector used in a meeting room and the like often projects an image from above a desk, which cannot always project the image onto a vertical wall but a distorted image is often displayed. The technique of adjusting the image to be rectangular by removing the distortion is the trapezoid correction (keystone correction). The trapezoid correction is to transform a trapezoid image into a rectangular image by performing a geometric transformation, such as contraction or enlargement, on the image signal to be projected.
During the trapezoid correction, a geometric blur is generated because the resolution partially lowers especially in the contraction. One technique to mitigate the geometric blur would be sharpness processing. In this regard, Patent Literature 1 discloses a technology of reducing the geometric blur caused by the enlargement or contraction in the trapezoid correction using the sharpness processing. Specifically, it describes dividing the screen into a plurality of regions, setting an adjustment value for the sharpness adjustment with respect to each region, and performing the sharpness adjustment on each region based on the adjustment value.